The present invention relates to a method of estimating diaphragm excursion of an electrodynamic loudspeaker. The electrodynamic loudspeaker may for example be mounted in a substantially acoustic sealed enclosure or ventilated enclosure of a portable communication device. The electrodynamic loudspeaker may be utilized for sound reproduction purposes, e.g. as a receiver for producing sound by acoustic coupling to the user's ear, or as a loudspeaker for playing recorded music or for voice reproduction in teleconferencing applications.
It is of significant interest to accurately estimate diaphragm excursion or displacement of an electrodynamic loudspeaker in a numerous sound reproduction applications and devices for the purpose of protecting the electrodynamic loudspeaker against mechanical damage. The diaphragm excursion must be accurately estimated to allow for a correspondingly accurate control of the diaphragm excursion. The accurate control or limiting of the diaphragm excursion is important to avoid the diaphragm or diaphragm assembly is driven above its maximum excursion limit which may happen if the diaphragm excursion is underestimated. If the maximum excursion limit is exceeded, various kinds to transitory or permanent mechanical damage may be imparted to the loudspeaker leaving the latter temporarily or permanently inoperative. The mechanical damage may be caused by collision between movable loudspeaker components, such as the voice coil, diaphragm or voice coil bobbin, and a stationary component of the loudspeaker such as the magnetic circuit. On the other hand, if the diaphragm excursion is overestimated and the excursion limitation therefore activated at an instantaneous excursion well below the maximum excursion limit of the loudspeaker in question, the maximum sound pressure of the loudspeaker is unduly restricted.
Since electrodynamic loudspeakers generally are rather non-linear devices, in particular at high sound pressure levels, with a large number of complex non-linearities it has proved difficult to accurately estimate the diaphragm excursion by various kinds of predictive model based approaches. In addition, parameter values of linear loudspeaker parameters of the electrodynamic loudspeaker, such as mechanical compliance and voice coil resistance, also vary slowly but markedly over time and temperature which leads to further challenges in maintaining an accurate model of the electrodynamic loudspeaker.
Hence, it is of significant interest and value to provide a relatively simple methodology for accurately estimating diaphragm excursion of the electrodynamic loudspeaker taking into account both the non-linear property of one or more loudspeaker parameters and the slowly time-varying property of the loudspeaker parameters. It would be advantageous compensate for the non-linear property of the one or more loudspeaker parameters without requiring time-consuming and costly individual characterization of the non-linearity of the electrodynamic loudspeaker during manufacturing of equipment or devices including the electrodynamic loudspeaker. The methodology of estimating the diaphragm excursion should preferably avoid complex computations to minimize the expenditure of computational resources of a signal processor implementing certain steps of the diaphragm excursion estimation methodology.